1. Field of the Invention
The invention relates to the field of gas turbine engines comprising at least two spools and comprising one or more stator stages in which the blades are variable-pitch blades.
The object of the invention is to optimize the angular position of said stator blades so as to reduce the fuel consumption when the turbine engine operates at steady speed. “Steady speed” means an engine speed at which the thrust provided by the engine is substantially constant over time.
2. Description of the Related Art
As an example, each spool of a twin-spool gas turbine engine comprises at least one compressor and one turbine mounted downstream of said compressor. By convention, in the present application, the terms “upstream” and “downstream” are defined relative to the direction of travel of the air in the turbine engine. Traditionally, a compressor comprises several rotor stages in order to accelerate and compress an air stream travelling from upstream to downstream in the engine. In order to straighten out the air flow after acceleration, a stator stage is arranged directly at the exit of each rotor stage.
A stator stage takes the form of a fixed wheel, extending axially, with radial stator blades mounted on the periphery of the stator wheel. In order to optimize the straightening of the air flow by the stator stages downstream of the rotor stages, it is possible to modify the angular orientation of the stator blades, the blades being called variable-pitch blades. Accordingly, the turbine engine comprises a system for controlling the angular position of the stator blades of the compressor.
Conventionally, with reference to the schematic FIG. 1A, the angular position of the stator blades of a twin-spool turbine engine M is determined mainly as a function of the rotation speed of the high-pressure rotor N2 and of the temperature at the entrance of the compressor T25. Accordingly, the control system comprises means 20 for computing a set value VSVCAL of the angular position of the blades on each stator wheel for a given rotation speed of the rotor N2. The computed set value VSVCAL is transmitted to a control actuator 6 arranged to modify the current angular position of the stator blades of the turbine engine M.
The computing means 20 are programmed by mathematical laws that have been previously determined in order to suit an “average” engine which is neither too recent (new engine straight out of the factory), nor too “worn” (ready for overhaul).
In practice, the real engine does not correspond to the “average” engine for which the mathematical laws have been computed. The mathematical laws of the current systems take account of the margin requirements of the engine (margins of robustness to aging, margins of dispersion from engine to engine, margins of fouling, etc.). The result of this is that the angular position of the blades is not optimized for the real engine but robust both for a new or for a degraded engine.
A solution would be to modify the mathematical laws so that the parameters of engine wear and the dispersions between engines are taken into account. However, this solution is difficult to apply, the parameters being numerous and difficult to model.